EP2313552B1 - Method for optimizing the energy balance in forming units in machines for producing fibrous webs and forming unit - Google Patents

Description

The invention relates to a method for optimizing the energy balance of a forming unit in a machine for producing fibrous webs, in particular paper, board or tissue webs, in which a pulp suspension introduced into the forming unit via a headbox after reaching the immobility point via at least two drainage devices within one led to the immobility point subsequent compression zone to a transfer area to a subsequent functional unit.

The invention further relates to a forming unit, comprising at least one, the fibrous suspension at least indirectly supporting endless endless belt and at least two series-connected or in the direction of flow of the pulp suspension within the compression zone successively arranged drainage.

The production of fibrous webs in a continuous production process takes place by forming fibers from an aqueous suspension on a moving sieve belt within the forming unit. In this case, the suspension and the train therefrom, the water due to the weight, by mechanical pressing, in particular due to the wire tension on curved dewatering elements and with the help of vacuum suction through the screen belt withdrawn. The fibrous web is transferred after the dewatering in the forming unit in a pressing device in which this water is further removed. The web is then transferred to a dry section where the drying process is completed. Forming units as part of a wet part of a machine for producing fibrous webs are known in a large number of designs from the prior art. These are subdivided in terms of their concrete execution in Einsiebformer and twin-wire former. Hybrid formers represent a variant of a twin-wire former with a four-wire screen, with the lower wire of the twin-wire former usually acting as a wire. The essential task of such forming units is firstly to achieve targeted deposition of the fibers next to and above one another and fiber orientation within the pulp suspension in the desired manner and also to dewater the pulp suspension during the passage through the forming unit such that at the end of the forming unit in the machine direction considers a fibrous web, which is characterized by a corresponding predefined dry content, can be transferred to the subsequent further processing units, in particular a press unit. In order to ensure a sufficient quality of the final product and to minimize the amount of final product to be discarded, the properties of the fibrous web must be continuously monitored in the production of material webs, in particular fibrous webs in paper or board machines. As a control variable of a control and / or regulation in the manufacturing process, different parameters can be set for this purpose, for example the basis weight, the water weight or also the thickness of a fibrous web in different sections within the machine for producing such fibrous webs. The final quality of the fibrous web is significantly influenced by the processes in the forming unit, such as the formation. In the prior art, there are a variety of control methods with which the fibrous web quality, which is expressed in terms of, for example, formation, porosity, fiber orientation, vertical sheet structure and moisture content, can be controlled by controlling the dewatering within the forming unit.

From the publication EP 1 426 488 A1 a device for producing a fibrous web is previously known, which has a twin-wire former, which together comprises co-operating screen belts, which are guided together to form a so-called double-wire zone over a portion of its circulation path. In this case, a measuring arrangement for measuring a property of the fibrous web is arranged in the region or in the vicinity of the twin-wire zone, wherein the measured property of a control unit is supplied as actual size and this control unit regulates a production parameter for the production of the fibrous web. In this case, the pressure level or the vacuum of a drainage device within a pre-dewatering zone is set by way of example as a controlled variable. On the basis of a nominal dry content of the fibrous web determined by the control unit, a drainage device of the pre-dewatering zone initially arranged in the direction of passage of the fibrous web can be used to set the dry content of the fibrous web even before the compacting zone. The main goal is the setting of a predefined formation.

From the publication EP 1 454 012 B1 a method for operating a forming unit is previously known, in which the consistency of stock within the forming unit, also the influence of consistency on the formation and / or porosity of the resulting fibrous web are determined and the consistency on the basis of the quality properties of the finished fibrous web and / or by optimizing a cost function. The quality property of the fibrous web is defined by the formation of this and / or the porosity. The cost function includes at least the costs associated with the required energy input and drive power.

From the publication EP 1 137 845 B1 is a method and a system for controlling the cross-section of the dry weight of a material web previously known, which is formed from a pulp suspension in a forming unit comprising at least one endlessly circulating water-permeable screen belt. In this case, an actual value of the dry weight of the fabric in the dryer section is determined and, based on a water weight transverse profile determined within the forming unit by means of water weight sensors, on a self-adjusting dry-weight cross-section closed. The pulp dry cross-section is controlled based on the dry pulp cross-profile predicted from the water weight measurement.

Among other things, all of the above-mentioned embodiments use the dewatering capacity at the dewatering devices within the forming unit as a controlled variable, in which case pressures, in particular negative pressures on suction devices, preferably act as controlled variables. In contrast, disclosed EP 1 063 348 A2 a possibility of control / regulation of drainage facilities in the form of formation strips.

The embodiments of the prior art essentially solve the task of controlling the individual components of a forming unit and / or to regulate or co-ordinate in their interaction such that in terms of the result to be achieved in relation to the resulting web, in particular fibrous web, optimal properties of the desired type can be achieved. This essentially does not take account of the cost aspect resulting from the energy balance of the entire system. In this case, a favorable energy balance usually contradicts the desired result, namely the achievement of a correspondingly high dry content after reaching or passing through the forming unit. In many systems, for example, the negative pressures to be applied to the individual suction devices within the forming unit are preset to a fixed value, with high-performance suction devices often being set to the maximum vacuum to be produced during operation. Accordingly high is the power requirement for drainage. Due to the relative movement between the movable screen belt and the high vacuum suction device, the screen belt is also subject to heavy wear due to the high frictional forces.

The invention is therefore based on the object to develop a method for optimizing the energy balance of a forming unit such that even at lower required energy input into the forming unit is achieved with respect to the required dry content optimum result while not affecting the sheet formation. The pulp suspension within the forming unit is to drain as energy-saving and wear-resistant until reaching the required dry content.

The solution according to the invention is characterized by the features of independent claim 1. Advantageous embodiments are described in the dependent claims. The forming unit is equipped according to the independent claim 12 with a corresponding control and / or regulating device.

An inventive method for optimizing the energy balance of a forming unit in a machine for producing fibrous webs, in particular paper, board or tissue webs, in which a introduced via a headbox in the forming unit pulp suspension after reaching the immobility point via at least two drainage devices within a at the Immobility point subsequent compression zone is led to a transfer area to a subsequent functional unit is characterized in that depending on a theoretically under system conditions maximum achievable dry content for a particular pulp suspension in the transfer area of the fibrous web to a downstream functional unit based on the existing drainage facilities, a target value for a target dry content to be set is set, which is chosen such that it is smaller than the theoretical h is the maximum achievable dry content under plant conditions, but is equal to or greater than a required minimum dry content in the area of the transfer area, and that the target dry content is controlled by reducing the initial solids content at least one of the last dewatering devices, preferably directly downstream of the last dewatering device within the compression zone Execution is regulated.

The theoretically maximum achievable / achievable dry content is understood to be the substance-dependent dry content of the fibrous web which can theoretically be achieved by utilizing the plant conditions, in particular maximum plant conditions. The plant conditions are characterized by process parameters of the operation of the individual dewatering devices and the entire forming unit, in particular the throughput speed. These also include the drying time at the individual dewatering elements, which can be determined as a function of the throughput speed of the pulp suspension and the length of the respective contact zone, and the process parameters of the individual dewatering devices / dewatering elements, in particular pressures or negative pressures. Depending on the substance in this context, the properties of the pulp suspension to be dehydrated, in particular its composition, water content, etc., means

This theoretically maximum achievable dry content is to be distinguished from the absolute maximum dry content, which corresponds to the dry content after an infinitely long drying time on one or the individual dewatering elements and is not feasible in practice.

Immobility point is understood to mean the local area within a forming unit, at which the individual fibers in the pulp suspension are aligned with one another in their position and can no longer move in relation to one another. This area also marks the beginning of the actual compression zone, i. it takes place in this no more formation, but only a dissolution of fluid, especially water from the forming of the suspension fibrous web.

Under drainage devices in the context of the invention, all stationary, movable or rotatable devices are understood, which allow by the application of forces, pulses and pressures and the application of a vacuum dewatering of the pulp suspension. These include, in particular, suction devices which are in the form of stationary suction boxes, curved or flat guide elements, such as Siebtische, Flachsaugeinrichtungen or rotatable rollers are present. The suction region is stationary, ie stationary and can be formed by one or more in the machine direction and across this across the entire web width extending and switchable in series suction zones, the individual arranged in series in the machine direction suction zones individually, in groups or together are switchable.

In a further embodiment, it is conceivable to subdivide the suction region also transversely to the machine direction into individual suction zones, which are likewise individually, in groups or jointly controllable.

The inventors have recognized that due to the characteristics of the dewatering behavior of the pulp suspension on or on a dewatering device, the initial dry solids content of the pulp suspension present at this end is not directly proportional to the input dry content and thus even a higher initial dry content can be set even with a lower input dry content at a dewatering device which is within the range of the maximum dry content theoretically achievable with this dewatering device under conditions of investment for the particular pulp suspension. This behavior is used specifically to save energy, by not necessarily a maximum utilization of the theoretically available power at all individual drainage facilities takes place, but only one of the last, preferably directly formed the last dewatering device in the compression zone and arranged so that it is suitable , to achieve a very high or even the maximum under plant conditions possible drainage performance and thus usually with very high or maximum energy input and thus maximum operating performance is operated while at least one or more of these upstream drainage facilities are operated within the compression zone such that the At this theoretically achievable material-dependent initial dry content is less than the maximum achievable achievable at full utilization of the available standing power. As a result, they can be operated with significantly lower energy input and thus lower power than to achieve the theoretically maximum possible dry content in cooperation with the last dewatering device, so that, for example in dewatering devices in the form of suction devices air volume savings in the double-digit percentage range are possible. At the same time the effect of the last dewatering device within the compression zone is reinforced with constant operating parameters to the effect that due to the now present at this inlet of the pulp suspension / fibrous web lower input dry content of energy input used to increased drainage performance and thus also to improve the lubricity due to consequent increased drainage. This makes it possible to use high-performance suction devices as one of the last or preferably directly as the last drainage device, wherein the use can be carried out wear-without additional measures.

In order to achieve a stable operating mode of a forming unit with respect to the dry content, it is not absolutely necessary to set the maximum dry content theoretically possible under plant conditions in a forming unit in the transfer area to the downstream functional unit, but it suffices to have a smaller predefined one depending on the operating and process conditions and adjust to the minimum dry content dependent on the dewatering pulp suspension. By exploiting the knowledge about the dewatering behavior of a dewatering device can then be achieved in the result, an optimal total dry content in the outlet from the forming unit while reducing the required energy input. As a result, the individual drainage elements can be operated much more effectively with regard to their energy balance. These require much less power, which can significantly reduce operating costs.

The input dry content at the last dewatering device may be controlled by controlling the dewatering performance of at least one of these within the Compression zone upstream drainage device can be adjusted. In a particularly advantageous embodiment, this is operated with a lower performance and thus drainage performance as maximum possible.

In order to ensure a stable and continuous operation of a forming unit in a machine for producing a fibrous web, the target dry content is controlled. For this purpose, an actual value of the target dry content behind the last dewatering element in the compression zone is determined continuously or periodically, compared with the desired value and depending on the difference, the individual control devices of the individual dewatering devices are controlled. The individual, the last drainage device within the compression zone upstream drainage devices act as actuators of this scheme whose operating parameters act as a controlled variable.

The target dry content to be set in the transfer area is chosen such that it deviates in a range from 0.1 to 5%, particularly preferably 0.1 to 3%, very particularly preferably 0.1 to 2%, of the theoretically achievable maximum dry content.

In terms of apparatus, the forming unit of a machine for producing fibrous webs comprises at least one endless circulating screen belt at least indirectly supporting a fibrous suspension and at least two drainage elements connected in series or in succession to the fibrous suspension within a compacting zone. Furthermore, a control and / or regulating system is provided, comprising a control and / or regulating device having at least one device for at least indirectly detecting a dry content of the fibrous web in a transfer area from the forming unit to a downstream functional unit at least indirectly characterizing size Device for specifying a desired value of a target dry content to be set and at least indirectly with the control devices of a single, one of Last drainage devices or the last drainage device within the compression zone upstream drainage device is connected. The control and / or regulating device further comprises a manipulated variable generator for forming the manipulated variables for controlling the individual drainage devices. As a device for at least indirectly detecting a dry content of the fibrous web in a transfer area from the forming unit to a downstream functional unit at least indirectly characterizing size, a sensor for direct detection or recording of a functionally related to the dry content size or by measuring the amount of dewatering, such as water weight sensors are used.

• Saugeinrichtung, insbesondere ortsfeste Saugeinrichtung oder rotierbare Siebsaugwalze;
• Formationskasten mit zumindest einer Saugzone und Formationsleisten ortsfest oder anpressbar;
• Formationsleisten; oder
• gekrümmtes Entwässerungselement.

Preferably, via the control and / or regulating device, the control of a plurality, preferably all dewatering devices, so that it is coupled to all adjusting devices of the individual drainage devices. The single drainage device may be designed as one of the following drainage devices:

• Suction device, in particular stationary suction device or rotatable Siebsaugwalze;
• Formation box with at least one suction zone and formation strips fixed or pressed;
• Forming blades; or
• curved drainage element.

In a particularly advantageous manner, one of the last drainage devices, preferably the last drainage device to be passed through a forming unit, is designed as a high-performance vacuum suction device. The upstream or upstream vacuum suction devices can then be operated with only a slightly reduced total dry content with significantly lower suction power. The solution according to the invention is particularly effective in terms of energy saving potential in embodiments of drainage devices, which include vacuum suction. It is conceivable, however also the application for other drainage elements, such as adjustable formation strips, where, for example, the contact pressure can be minimized.

The solution according to the invention is explained below with reference to figures. It details the following: FIGS. 1a and 1 b illustrate in a schematic simplified representation of an embodiment of a forming unit according to the invention and one of these associated control / regulating system, an inventive method for controlling the dry content; FIG. 2a illustrates by means of a signal flow diagram a method for controlling the dry content; FIG. 2b illustrates by means of a signal flow diagram a method for controlling the dry content; FIGS. 3a and 3b illustrated by diagrams of the operation of the solution according to the invention; FIGS. 4a and 4b illustrate exemplified possible configurations of a forming unit following the immobility point suitable for use of the method according to the invention with reference to a section of this; FIGS. 5a and 5b illustrate by way of example further possible configurations of a forming unit following the immobility point suitable for use of the method according to the invention with reference to a section of this; Figures 6a and 6b illustrate by way of example possible third configurations of a forming unit following the immobility point suitable for use of the method according to the invention with reference to a section of this; Figure 7a a schematic sectional view of a first embodiment of a dewatering device in the form of a Siebsaugwalze for the forming unit according to the invention; FIG. 7b a schematic sectional view of a second embodiment of a dewatering device in the form of a Siebsaugwalze for the forming unit according to the invention; FIG. 8a a schematic sectional view of a first embodiment of a dewatering device in the form of a high vacuum suction for the forming unit according to the invention; and FIG. 8b a schematic sectional view of a second embodiment of a dewatering device in the form of a high vacuum suction for the forming unit according to the invention.

The FIGS. 1a and 1b illustrate in schematic highly simplified representation based on an exemplary embodiment of a forming unit 1 and a control / regulating system 4, the basic principle of a method according to the invention for optimizing the energy balance within the forming unit 1 in a machine 2 for producing webs, in particular in the form of fibrous webs F in shape of paper, cardboard or tissue webs. Schematically shown in simplified form FIG. 1a to a forming unit 1, which is preceded by a headbox 3, via which a pulp suspension FS of the forming unit 1 is supplied. To clarify the individual directions, a coordinate system is applied to the forming unit 1. The X-direction describes the direction of the guidance of the pulp suspension FS and thus the provided within the machine 2 for the production of fibrous web passage direction for the material web formed therefrom, which is also referred to as the machine direction MD. The direction perpendicular to this in the same horizontal plane describes the Y-direction, which corresponds to the cross-machine direction MD and is referred to as the CD direction. The Z direction perpendicular to both aforementioned directions describes the vertical direction.

In the forming unit 1, the pulp suspension FS is guided on at least one endlessly circulating screen belt 11.1, in the case shown at least over a partial area between two endlessly rotating screen belts 11.1 and 11.2, filtered and thickened and from reaching a so-called immobility point IP in the subsequent compression zone VZ compacted. Between the head box 3 and a transfer area 5, in which the fibrous web F is transferred to a press unit 6 downstream of the forming unit 1, the forming unit 1 in the form of a hybrid former comprises in the illustrated case, by way of example, three dewatering sections S1 to S3, which are connected in series and one after the other be traversed by the pulp suspension FS. These are structured differently. The first dewatering section S1 in the direction of passage forms a so-called predewatering zone 10, the subsequent dewatering section S2 is referred to as twin-wire zone 12, while the dewatering section S3 forms a post-dewatering section 13. The screen belt 11.1 is part of all drainage routes S1 to S3. In the individual zones 10, 12 and 13, drainage devices E1 to En are at least indirectly effective on the pulp suspension FS. Within the pre-dewatering zone 10, a breast roll 14 is provided following the headbox 3 in the first endlessly circulating wire 11.1. The shot of the pulp suspension FS takes place directly on a, in a horizontal plane arranged Siebtisch as dewatering unit E2, which is supported by the sieve belt 11.1 formed Langsiebanordnung. The dewatering takes place via the dewatering section S1 and thus the pre-dewatering zone 10. The fibrous suspension FS is further guided and dewatered via the second dewatering section S2, which is formed by the twin-wire zone 12. For this purpose, the screen belt 11.1 is guided together with a further, second, endlessly circulating screen belt 11.2 in the form of a top wire belt over part of its circulation path to form the dewatering path S2. In the dewatering section S2, at least one dewatering device E3 is arranged, which is effective on at least one of the screen belts, preferably both screen belts 11.1 and 11.2 and the fibrous suspension FS guided therebetween. The separation between the first and the second screen belt 11.1 and 11.2 is carried out downstream of the dewatering device E3, which can be provided to support the separation of suction, for example in the form of curved vacuum cleaner or drainage E3 is provided with a correspondingly trained suction zone. The dewatering device E3 consists of a arranged in the sieve belt 11.2 dewatering box 15 and in the screen belt 11.1 in the region of the extension of the dewatering 15 in Siebumlaufrichtung Siebbands 11.2 viewed formation box 16. The dewatering box 15 and the formation box 16 contain so-called formation strips, preferably in the Formation box 16 contained formation strips 16.1 to 16.n are mounted on the inner surface of the screen belt 11.1 against this pressed. The individual formation strips 16.1 to 16.n in the formation box 16 are preferably individually, in groups or can be pressed together. The formation strips 16.1 to 16.n are preferably guided individually and viewed one behind the other in the wire direction, preferably arranged parallel to one another and extend over the machine width. The drainage box 15 forms the drainage device E3.2, the formation box 16 the drainage device E3.1. The contact pressure of the formation strips 16.1 to 16.n via an adjusting device 9.31. Drainage box 15 and / or formation box 16 are further evacuated, wherein the aspiration in the direction of extension in the machine direction MD viewed over a suction zone or a plurality of successively connected and individually or in groups can be controlled suction zones. Within the twin-wire zone 12, the immobility point IP sets for the fibers in the pulp suspension FS. This marks in the machine direction MD, the location at which the fibers of the pulp suspension FS are aligned due to the dewatering that now no longer change their orientation and remain in position to each other, with a further action of drainage facilities only for further drainage under Compaction leads, which is why the point of immobility subsequent functional area is referred to as compression zone VZ. This local area is provided within the dewatering section S2 and extends across the width of the forming unit 1.

Downstream of the twin-wire zone 12 is the post-dewatering zone 13, which is connected in series and successively contains the dewatering devices E4, En-1 and En, where En forms the last dewatering device upstream of the transfer area 5. The individual drainage devices E4 to En may preferably be in the form of suction devices. The post-dewatering zone 13 is formed by the first screen belt 11.1. The forming unit 1 thus comprises at least one, preferably a plurality of drainage devices E1 to En acting in series or in parallel.

Before the transfer area 5, the resulting fibrous web F has a dry content TG, which is referred to as the final dry content of the forming unit 1. This is usually specified and corresponds to the set dry content TG at the end of the forming unit 1. Depending on the investment conditions, such as speed of the machine for producing fibrous webs F and the selected dewatering E1 to En and their operating parameters can for a particular pulp suspension, ie a Fasoffoffsuspension with certain properties, such as composition, consistency, etc. theoretically a maximum final dry content TG _max at the end of the forming unit 1, in particular in the transfer area 5 or before this be achieved following the last drainage device En. This theoretically maximum dry content TG _max for a particular pulp suspension type is achieved when all the drainage devices E1 to En are operated by exploiting their maximum possible power with the maximum possible exposure time. However, it has been found that, by solely increasing the energy input and thus the power of the individual drainage devices E1 to En over the period of action of the latter, it is not necessarily the case that a dewatering increase within the forming unit 1 corresponding to this is achieved. The inventors have recognized that slightly _max of TG deviating lower dry content TG _target in the exit region 17 of the forming unit 1, that is in or before the transfer region 5 after the last dewatering device En also be achieved if the performance of each drainage facilities, in particular those of the last in Passage direction arranged drainage device arranged upstream of E and the immobility point IP, here E4 to En-1 with n element of the natural numbers does not correspond to their theoretically available maximum power, so that the theoretically maximum available drainage capacity at the last drainage device En can be fully utilized. In this case, a targeted dry content TG _{target of} the fibrous web F for the outflow region 17 of the forming unit 1 is predefined, which ranges from about 0.1 to 5%, preferably 0.1 to 3%, very particularly preferably 0.1 to 2%. deviates from the theoretically maximum achievable and substance-dependent dry content TG _max under plant conditions. This is set as setpoint X _set -TG _target . The current is adjusting the actual value X _{Is target} TG at the outlet 17 of the forming unit 1 is detected by means of a device 7 for the at least indirect detection of the dry content of TG at least indirectly characteristic. This device 7 is preferably assigned directly to the web guide in the outlet region 17 of the forming unit 1 and is designed in the simplest case as a sensor. The desired value is processed in a control and / or regulating device 8 and set by driving at least one, preferably at least the, the last drainage device En directly upstream drainage device En-1. For this purpose, the control and / or regulating device 8 with the adjusting device or the adjusting devices 9.1 to 9.n-1 of each, the last arranged within the forming unit 1 in the direction of flow of the pulp suspension FS drainage device En upstream drainage devices E1 to En-1 coupled. These are preferably controlled as a function of the goal to be achieved dry content X _target TG _target in dependence of the actually existing actual value in such a way that the actual value X _Is TG _target corresponds to the target value X _{set target} TG. The control takes place in such a way that the dewatering power at the drainage device upstream of the dewatering device En and downstream of the immobility point IP En-1 or the other upstream drainage devices E4 to En-1 is lowered, so that each set at the outlet of these individual drainage E4 to En-1 a lower dry content than when fully exploiting the drainage at the individual drainage E4 to En-1. In this case, the individual drainage devices E4 to En-1 arranged after the immobility point IP and before the last drainage device En act as setting devices of a control / regulation 4 of the target dry content TG _target .

FIG. 1b exemplifies the input and output variables at the, associated with the forming unit 1 control and / or regulating device 8. As the input X is at least the target value for the targeted dry content X _target -TG _goal , in addition to a control the actual value X _actual - TG _Goal . While maintaining the conditions at the last drainage device En, in particular setting the maximum drainage capacity at this by controlling the associated adjusting device 9.n to form a corresponding manipulated variable Y9.n the other manipulated variables Y9.4 and / or Y9.n-1 are determined and the actuators 9.4 and / or 9.n-1 driven.

The FIG. 2a illustrates the basic principle of the method according to the invention on the basis of a signal flow diagram. This shows the knowledge or the determination of the maximum dry content TG _max , which _{can be} achieved _{theoretically} within the forming unit 1 with the available drainage devices E1 to En in their combination in application with optimum utilization of the theoretically available drainage capacity P _max . Depending on the theoretically maximally achievable substance-dependent dry content TG _max under plant conditions, a _target dry content TG _target to be achieved is set for the operation of the forming unit 1, which is determined as a function of TG _max . This corresponds, as already stated, a value which is in the range of 0.1 to 5%, preferably 0.1 to 3%, very particularly preferably 0.1 to 2% of the actual theoretically possible maximum Dry content TG _max deviates. The target dry content TG _target is less than the maximum dry content TG _max .

Furthermore, the target dry content TG _{target is set} as target value X _target -TG _{target of} a controller, preferably a controller. FIG. 2a exemplifies only the control. Here, depending on the determined or predetermined target values X _target -TG _target, an activation of at least one of the last drainage device En of the forming unit 1 upstream drainage device En-1 to En-x and thus a specification of the manipulated variables Y9.n-1, x = f ( X _target -TG _target ), where x corresponds to the maximum number of drainage devices E within the compression zone VZ.

The FIG. 2b illustrates the integration of the controller according to the invention in a control, wherein in addition to the setpoint specification X _target -TG _target the current actual value Xist-TG _{target is} continuously determined and the individual manipulated variables Y9.n-1, x for controlling the last drainage device upstream drainage facilities En-1 to En-x are formed. The last drainage device En in the direction of flow is operated with the maximum possible drainage capacity. The manipulated variable Y9.n for driving is constant, ie remains unchanged or is set according to the maximum power. By means of the continuous comparison, the drainage behavior at the drainage devices upstream of the last drainage device En-1, x can be controlled and regulated in such a way that they are lowered with respect to their drainage performance and the maximum possible dewatering effect is achieved with the last possible drainage effect with the last drainage device En becomes.

mit

TG_E-aus

Ausgangstrockengehalt an der Entwässerungseinrichtung E;

TG_E-ein

Eingangstrockengehalt an der Entwässerungseinrichtung E;

TG_∞

theoretisch erreichbarer stoffabhängiger Trockengehalt an einem Entwässerungselement bei unendlicher Einwirkdauer, insbesondere Saugzeit;

k

Stoffkonstante; und

t_saug

Saugzeit am betrachteten Entwässerungselement E.

The inventors use the knowledge that the dry content development in the sheet compaction zone can be described at a given vacuum level at a dewatering device E in the form of suction devices and thus the dewatering effect by an expotential function. This is for the single drainage device E as follows and is exemplary in FIG. 3a represented by a diagram: $${\mathrm{TG}}_{\mathrm{e}\mathrm{-}\mathrm{out}}\mathrm{=}{\mathrm{TG}}_{\mathrm{e}\mathrm{-}\mathrm{one}}\mathrm{+}\left({\mathrm{TG}}_{\mathrm{\infty }}\mathrm{-}{\mathrm{TG}}_{\mathrm{e}\mathrm{-}\mathrm{one}}\right)\mathrm{x}\left(\mathrm{1}\mathrm{-}{\mathrm{e}\mathrm{-}}^{\mathrm{suction\; xk}}\right)$$

With

TG _E-out

Initial dry content at the dewatering device E;

TG _E-one

Initial dry matter content at the dewatering device E;

TG _∞

theoretically achievable substance-dependent dry content of a dewatering element at infinite exposure time, in particular suction time;

k

Material constant; and

t _suction

Suction time at the considered drainage element E.

In this case, starting from a low input dry content TG _E-an , the dry content TG of the pulp suspension FS or of the fibrous web F present at the respectively considered dewatering device E initially increases very rapidly with the suction time. Due to the exponential characteristics of the drainage behavior, however, the slope of the dewatering intensity decreases progressively, that is, the dry content increase per time interval is reduced. The dry content TG asymptotically approaches over the theoretically achievable absolutely dry content TG _∞ at this dehydrator E after endless dry season, especially on suction time. This corresponds to the dry content TG∞, which is achieved at infinite suction time at the individual drainage device. Changes in the input dry matter TG _E-one therefore do not significantly affect the initial dry matter content TG _E- out. Practically, however, an infinitely long exposure time and thus drying time is not feasible. Therefore, the single dewatering device is operated in the prior art with maximum dewatering power, wherein over the operating time t _operation , which corresponds to the exposure time a theoretically maximum dry content TG _{max is} achieved. The Inventors have now recognized that the behavior can be optimally exploited to operate the entire system described more effectively and in particular more energy efficient by a less than the theoretically maximum achievable dry content TG _{max is set} as the _target dry content TG _target to reach, which still one permissible minimum dry content at the outlet from the forming unit 1 corresponds. This is controlled, preferably adjusted.

The FIG. 3b 3 illustrates a concrete example of a dry content development in a forming unit 1 within a sheet compacting zone VZ comprising by way of example a two-zone suction suction roll in the form of a combined dewatering device with a subsequent dewatering device En in the form of a high vacuum suction device. The individual suction zones of the suction sieve are referred to as drainage devices E4 and E5. The guide speed of the fibrous web F is exemplified 2000 m / min. The dry _content TG _E4,5-a before the sieve suction roll with the individual suction zones E4, E5 is constantly 8%. When applying the respective maximum vacuum levels at the dewatering devices E4, E5, in the first zone with 30 kPa and in the second zone with 60 kPa example operated, resulting in accordance with the characteristic curve I is a starting dry content TG _{E4, E5-out} of 14.6% , With the drainage device En in the form of a high-vacuum suction, which is exemplarily operated at 65 kPa and thus the maximum power, a dry content of 19.6% is achieved. This dry content TG _En-aus corresponds to the achievable substance-dependent maximum dry content TG _max under plant conditions at the outlet of the forming unit 1. As the minimum dry content for maintaining stable operation and thus target dry content TG _target , 19% is set here for the control according to the invention. The resulting characteristic is indicated in the diagram by II. With the same input _{dry content} TG _E4,5-an of 8%, the performance at the drainage facilities E4 and E5 can be reduced. The vacuum level in the first zone and thus at E4 is 25 kPa, at the second dewatering device E5 55 kPa. The achievable initial dry _{matter content} TG _{E4, E5-Aus} and thus input _{dry matter content} TG _En-one at the drainage facility En is reduced to 13.3% compared to I. The large drop in dry content at the suction sieve roller is partly compensated by the following drainage device En. With the same performance, the drainage performance of En En increases, thereby allowing better lubrication between the screen belt and the drainage device En.

The FIGS. 4a and 4b illustrate exemplified by means of sections of a former unit 1 arrangements of the individual drainage elements E1 to En, the immobility point IP and the site for the _target dry content TG _goal . Are recognizable in the FIG. 4a in a section of a twin-wire zone 12, a dewatering unit E1 of two on both sides of the sides of the fibrous suspension FS leading screen belts 11.1, 11.2 becoming effective drainage E1.1 and E1.2, wherein one of the two drainage E1.1, E1.2 is designed as a drainage box 15, to which a vacuum can be applied and the other second dewatering E1.2 with elastic formation strips 16.1 to 16.n, which are effective at the carrying of the pulp suspension FS side facing away from the screen belt 11.2, is executed. These are used to apply pressure pulses in the pulp suspension FS. After passing through the dewatering device E1, the immobility point IP is reached and the fibrous web F arising from the pulp suspension FS is conveyed via individual further dewatering devices E2 in the form of a suction device, E3 in the form of a suction sieve and En-1 in the form of a suction device and the last suction device arranged in the direction of flow En drained. In this case, the dewatering behavior at the individual dewatering elements E2 and / or E3 and / or En-1 can be controlled to set the _target dry content TG, in order to achieve a lower input dry content at the inlet to the last dewatering element En.

In contrast, illustrates the FIG. 4b an embodiment according to FIG. 4a in which the drainage element En-1 was omitted. Here, the control is essentially on the now the last drainage device An upstream drainage device En-1 in the form of a suction sieve.

FIG. 5a illustrates a section of a forming unit 1 with twin-wire zone 12 and subsequent Nachentwässerungszone 13, wherein the twin-wire zone 12 is at least partially shown, comprising here a dewatering unit E1 from an upper dewatering E1.2 and arranged in the lower wire belt 11.1 drainage E1.1 with strip-shaped Elements 16.1 to 16.n for introducing pressure pulses in the guided between the two endlessly rotating screen belts 11.1 and 11.2 pulp suspension FS. Within the dewatering section S1 formed by the twin-wire zone 12, a drainage device E2 in the form of a suction device also follows. Within the subsequent dewatering section S2 in the form of a post-dewatering zone 13, the dewatering devices E3, En-1 and En with their adjusting devices 9.3, 9.n-1 and 9.n are arranged. The control of the drainage behavior takes place here mainly via the control of either the drainage device En-1 and / or E3 and / or E2.

In contrast, illustrates the FIG. 5b an alternative embodiment of the formation of a twin-wire zone 12, in which, following the dewatering device E1 from E1.2 in the form of a dewatering box 15 and E1.1 in the form of a formation box 16 in the screen belt 11.1 a suction device is arranged, comprising two suction zones forming the dewatering devices E2, E3 and spaced therefrom after separation of the two sieve bands 11.1, 11.2 in the fibrous web guiding wire 11.1 the dewatering device En-1 and then a Siebsaugwalze as dewatering En.To achieve the target dry content TG _target behind the last dewatering element En in the form of Siebsaugwalze the input dry content is controlled at this by controlling the dewatering behavior on at least one of the individual dewatering elements E2 to En-1.

The Figures 6a and 6b illustrate exemplified further embodiments of a forming unit 1, comprising a dewatering E1.1 in the form of a suction sieve suction and arranged on the bottom wire drainage E1.2 and then spaced therefrom arranged drainage elements E2 to En, wherein E2 to E4 are formed by individual suction devices, while En-1 is formed by a suction roll and En in turn by a suction device. The FIG. 6b illustrates an alternative embodiment with a reduced number of drainage devices E2 and E3 compared FIG. 6a wherein the dewatering device E1.2 has a different number of Siebsaugzonen.

The Figure 7a shows a schematic sectional view of a first embodiment of a dewatering device E3 in the form of a Siebsaugwalze for the invention and in the FIGS. 4a, 4b . 6a and 6b illustrated and described forming unit. 1

The suction sieve shown and well-known to those skilled in the art has, purely by way of example, two suction zones which, based on the FIG. 3b denoted by E4 and E5. Of course, it can also have more than two suction zones. The two immediately adjacent suction zones E4 and E5 are separated from each other by means of a common main partition 18. The mutual limitation of the respective suction zone E4 and E5 is effected by means of a respective movable secondary partition 19.4 and 19.5. If the respective side partition wall 19.4 and 19.5 is arranged in its end position, then each of the two suction zones E4 and E5 has an open area of 100%. By a movement (arrow) of the respective secondary partition 19.4 and 19.5, the respective open area of the individual suction zone E4 and E5 can be set in a range of 100% to 0%. The movement (arrow) of the respective secondary dividing wall 19.4 and 19.5 can take place in a known manner by means of a respective actuating device 9.4 and 9.5 which can be acted upon by the control and / or regulating device. By way of example, the two side walls 19.4 and 19.5 are also after one shown movement dashed lines, wherein the first suction zone E4 then still has an open area of about 30% and the second suction zone E5 then still has an open area of about 50%.

The FIG. 7b shows a schematic sectional view of a second embodiment of a dewatering device E3 in the form of a Siebsaugwalze for the invention and in the FIGS. 4a, 4b . 6a and 6b illustrated and described forming unit. 1

The suction sieve shown and well-known to those skilled in the art has, purely by way of example, two suction zones which, based on the FIG. 3b denoted by E4 and E5. Of course, it can also have more than two suction zones. The two immediately adjacent suction zones E4 and E5 are separated from each other by means of a common main partition 18. The mutual limitation of the respective suction zone E4 and E5 is carried out by means of a respective side partition 19.4 and 19.5. The respective suction zone E4 and E5 has a maximum open area of 100%. Furthermore, a cover plate 20.4 and 20.5 is provided for each of the two suction zones E4 and E5, by means of which the open area of the associated suction zone E4 and E5 can be reduced to 0%. The individual cover plate 20.4 and 20.5 is arranged inside the respective suction zone E4 and E5 movable (arrow). The movement (arrow) of the respective cover plate 20.4 and 20.5 can take place in a known manner by means of a respective actuatable by the control and / or regulating device 9.4 and 9.5.

The FIG. 8a shows a schematic sectional view of a first embodiment of a dewatering device E6 in the form of a high vacuum suction for the invention and in the FIGS. 1a . 4a, 4b . 5a, 5b . 6a and 6b illustrated and described forming unit. 1

The illustrated and the expert well-known high-vacuum suction device has purely by way of example a suction zone E7, the top side with a guided sieve contacting suction pad 21 is provided. The suction pad 21 may be perforated, slotted or arbitrarily open structured in a known manner and it has a maximum open area of 100%. Furthermore, a cover plate 22.6 is provided, by means of which the open surface of the Saugerbelags 21 can be reduced to 0%. The cover plate 22.6 is arranged on the inside of the suction zone E7 movable (arrow). The movement (arrow) of the cover plate 22.6 can in a known manner by means of an actuatable by the control and / or regulating device 9.4. respectively

The FIG. 8b shows a schematic sectional view of a second embodiment of a dewatering device E6 in the form of a high vacuum suction for the invention and in the FIGS. 1a . 4a . 4b . 5a . 5b . 6a and 6b illustrated and described forming unit. 1

The illustrated and well-known to the skilled high vacuum cleaner has purely by way of example a suction zone E7, which is provided on the upper side with a guided sieve touching the suction pad 21. The suction pad 21 may be perforated, slotted or arbitrarily open structured in a known manner and it has a maximum open area of 100%. Furthermore, at least one means 24 for reducing the open areas is provided for each opening 23 of the sucker pad. The means 24 may, for example, be a bellows 25, which may be acted upon by an actuating device 9.4 which can be acted upon by the control and / or regulating device. can be acted upon. By means of the means 24, the open area of the Saugerbelags 21 can be reduced to 0%.

LIST OF REFERENCE NUMBERS

1 forming unit 2 Machine for producing material webs 3 headbox 4 Control / regulating system 5 Transfer area 6 press unit 7 Device for the at least indirect detection of a dry content at least indirectly descriptive size 8th Control and / or regulating device 9.1 - 9.n setting device 9.4 setting device 9.5 setting device 10 pre-dewatering 11.1,11.2 screen belt 12 twin 13 Nachentwässerungszone 14 breast roll 15 dewatering box 15.1, 15.2 suction zone 16 forming box 16.1-16.n formation strips 17 discharge area 18 main partition 19.4 In addition to partition 19.5 In addition to partition 20.4 cover 20.5 cover 21 suction pad 22.6 cover 23 opening 24 medium 25 bellows CD Direction transverse to the machine direction E1-E5, En-1, En dehydrator En.1.2, En-1.1, En-1, x dehydrator E1.1, E1.2, E3.1, E3.2 dehydrator E3 Drainage device (suction sieve roller) E4 suction zone E5 suction zone E6 Drainage device (high vacuum suction) E7 suction zone F Fibrous web FS Fibrous suspension IP immobility k material constant MD machine direction S1 - S3 dewatering section t _suction Suction time at the considered drainage element E t _operation Duration of action on the considered drainage element E TG _E-out Starting dry content at a drainage device E TG _E-one Input dry content at a drainage device E TG _En-one Initial dry matter content at a drainage facility En TG _E4,5-one Input dry matter content at a drainage facility E4, E5 TG _En-out Initial dry matter content at a drainage facility En TG _E4,5-off Dry solids content at a dewatering device E4, E5 TG _max Theoretically maximum achievable substance-dependent dry content in the outlet area of the forming unit TG _∞ Theoretically achievable substance-dependent dry content of a dewatering element with infinite duration of action, in particular suction time TG _goal Target dry content in the outlet area of the forming unit VZ compression zone Xsoll-TG _goal Target dry solids content in the discharge area of the forming unit Xist-TG _goal Actual target dry content in the discharge area of the forming unit Y1-Y4, Yn, Yn-1, x manipulated variable X, Y, Z coordinates

Claims (14)

1. Method for optimizing the energy balance of a forming unit (1) in a machine (2) for producing fibrous webs (F), in particular paper, board or tissue webs, in which a fibrous suspension (FS) introduced into the forming unit (1) by a headbox (3), after reaching the point of immobility (IP), is led over at least two dewatering devices (E2 to En) within a consolidation zone (VZ) following the point of immobility to a transfer region (17) to a following functional unit (6),
   characterized in that
   depending on a maximum dryness (TG_max) theoretically achievable under plant conditions in the area of the transition region (17) of the fibrous web (F) to the downstream functional unit (6), on the basis of the dewatering elements (E1-En) that are present, a setpoint value for a target dryness (X_soll-TG_Ziel) to be set is predefined, which is chosen in such a way that this is less than the maximum theoretically achievable dryness (TG_max) but equal to or greater than a required minimum dryness in the area of the transition region (17), and that the target dryness (TG_Ziel) is controlled by reducing the input dryness (TG_E-ein) on one of the last dewatering devices (En) arranged in the guide direction of the fibrous suspension (FS) within the consolidation zone (VZ).
2. Method according to Claim 1,
   characterized in that
   the target dryness (TG_Ziel) is controlled by reducing the input dryness (TG_E-ein) on the dewatering device (En) arranged last in the guide direction of the fibrous suspension (FS) within the consolidation zone (VZ).
3. Method according to Claim 1 or 2,
   characterized in that
   the input dryness (TG_E-ein) on at least one of the last dewatering devices (En) arranged in the guide direction of the fibrous suspension (FS) or the last dewatering device (En) is set by controlling the dewatering performance on at least one dewatering device (E2 to En-1) arranged upstream of the latter within the consolidation zone (VZ).
4. Method according to one of the preceding claims,
   characterized in that
   the operating parameters of a dewatering device (E2 to En-1, En-1, x) arranged upstream of the last dewatering device (En) arranged in the guide direction of the fibrous suspension (FS) or of the last dewatering device (En) are set in such a way that the said dewatering device (E2 to En-1, En-1, x) is operated with a lower dewatering performance than the maximum possible.
5. Method according to one of the preceding claims,
   characterized in that
   the target dryness (TG_Ziel) is regulated.
6. Method according to one of the preceding claims,
   characterized in that
   an actual value of the target dryness (X_ist-TG_Ziel) after the last dewatering element (En) is determined continuously or periodically, is compared with the setpoint value (X_soll-TG_Ziel) and the individual actuating devices (9.1-9.n-1) of the individual dewatering devices (E1 to En-1, En-1, x) are activated as a function of the difference.
7. Method according to one of the preceding claims,
   characterized in that
   a target dryness (TG_Ziel) is predefined which deviates from the theoretically achievable maximum dryness (TG_max) in the range from 0.1 to 5%, particularly preferably 0.1 to 3%, quite particularly preferably 0.1 to 2%.
8. Method according to one of the preceding claims,
   characterized in that
   the dewatering device (E2 to En-1, En-1, x) arranged upstream of one of the last dewatering devices (En) arranged in the guide direction of the fibrous suspension (FS) or of the last dewatering device (En) within the consolidation zone (VZ) is implemented as a suction device, in particular a stationary suction device or rotating wire suction roll.
9. Method according to one of the preceding claims,
   characterized in that
   one of the last dewatering devices (En) arranged in the guide direction of the fibrous suspension (FS) or the last dewatering device (En) is implemented as a stationary suction device, in particular a stationary high-vacuum suction device, or as a rotating wire suction roll, in particular a high-vacuum wire suction roll.
10. Method according to either of Claims 8 and 9,
    characterized in that
    at least the vacuum that can be applied is adjustable.
11. Method according to one of Claims 8 to 10,
    characterized in that
    the dewatering devices (E1-En, En-1, En-1, x) implemented as a stationary suction device or rotating wire suction roll comprise at least one, preferably a plurality of suction zones (15.1, 15.2) aligned in the machine direction (MD) and/or transversely with respect to the machine direction (MD), which can be activated individually, in groups or jointly.
12. Forming unit (1) of a machine for producing fibrous webs (F), comprising at least one endlessly circulating wire belt (11.1, 11.2) at least indirectly supporting a fibrous suspension (FS), and at least two dewatering devices (En-1, En-1, x, En) connected in series and arranged one after another in the passage direction of the fibrous suspension (FS) within a consolidation zone (viz),
    characterized in that
    a control and/or regulating system (4) is provided, comprising a control and/or regulating apparatus (8) which is connected to at least one device (7) for the at least indirect measurement of a variable at least indirectly characterizing the dryness (X_ist - TG_Ziel) of the fibrous web (F) in a transition region (5) from the forming unit (1) to a downstream functional unit (6), to a device for predefining a setpoint value of a target dryness (X_soll-TG_Ziel) to be set, and at least indirectly to the actuating devices (9.1 to 9.n-1) of an individual dewatering device (E2 to En-1, En-1, x) connected upstream of one of the last dewatering devices or the last dewatering device (En) within the consolidation zone (VZ), and an actuating variable former for forming the actuating variables (Y9.1 to Y9.n) of the individual dewatering devices (E1 to En).
13. Forming unit (1) according to Claim 12,
    characterized in that
    the control and/or regulating apparatus (8) is coupled to the actuating devices (9.1 to 9.n) of the individual dewatering devices (E1 to En).
14. Forming unit (1) according to Claim 12 or 13,
    characterized in that
    the individual dewatering device (E1 to En) is implemented as one of the following dewatering devices:

    - a suction device, in particular a stationary suction device or rotatable wire suction roll;

    - a forming box having at least one suction zone and forming foils that are stationary or can be pressed on;

    - forming foils; or

    - a curved dewatering element.

Images